A089992 - OEIS

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A089992

Second prime divisor of numbers that are not powers of primes (A024619).

3, 5, 3, 7, 5, 3, 5, 7, 11, 3, 13, 7, 3, 11, 17, 7, 3, 19, 13, 5, 3, 11, 5, 23, 3, 5, 17, 13, 3, 11, 7, 19, 29, 3, 31, 7, 13, 3, 17, 23, 5, 3, 37, 5, 19, 11, 3, 5, 41, 3, 17, 43, 29, 11, 3, 13, 23, 31, 47, 19, 3, 7, 11, 5, 3, 13, 5, 53, 3, 5, 37, 7, 3, 23, 29, 13, 59, 17, 3, 61, 41, 31, 3, 43

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A119288(A024619(n)). - Amiram Eldar, Apr 12 2021

MATHEMATICA

Select[Table[If[Length[(f = FactorInteger[n])] > 1, f[[2, 1]], 1], {n, 1, 150}], # > 1 &]

PROG

(PARI) f(n) = a=factor(n); v=a[, 1]; ln=length(v); if(ln>1, return(v[2]));

g(m) = for(x=2, m, if(f(x)>0, print1(f(x)", ")));